The present invention relates to a method of and apparatus for synthetic testing of a multi-break circuit breaker, wherein the interrupter units are enclosed within, insulated from and supported by a metallic tank.
In recent years, the voltage and the capacity of power transmission systems are becoming higher and higher to a point where a transmission line of 1100 KV is envisaged. In keeping step therewith, interrupting or breaking capacity of circuit breakers is becoming higher. As a result, it is increasingly difficult to test the breaking performance of all the interrupter units because of the insufficient capacity of the testing equipment. From this point of view, it has been a practice to resort to a unit testing method wherein only one interrupter unit is tested as to the breaking performance, and the voltage used for the test is multiplied by a constant related to the voltage share and the number of the interrupter units, and the result is regarded equivalent to the result of testing all the interrupter units.
The unit testing method is valid when testing a porcelain-clad circuit breaker which is not associated with the problem of production of heated gas due to an arc in the interrupter unit which impairs the insulation between the interrupter unit and the ground potential element. But with a multi-interrupter circuit breaker having interrupter units enclosed in, insulated from and supported by a metallic tank, heated gas which has passed through the arc and has its insulation strength lowered is blown into the space between the tank and an end of the series connection of the interrupter units. If a transient recovery voltage to test the performance of a single interrupter unit only is applied in accordance with the unit testing method, performance of the interrupter units may be properly tested, but the insulation between the tank and the end of the series connection immediately after the interruption is not properly tested.
FIG. 1 shows an arrangement used for implementing another conventional method. FIG. 2 shows the voltages and current appearing at various portions in the arrangement shown in FIG. 1. A multi-break circuit breaker 1 to have its breaking performance tested has, for example, four series-connected interrupter units 11-14. The series connection S of the interrupter units 11-14 is insulated by porcelain insulators 2 from a tank 3. The tank 3 itself is insulated by insulating support members 4 from the ground. One end Sg of the series connection S is connected to a lead conductor 5 to the ground. The other end Sn is connected by another lead conductor 6 to a large current source 17 including a short-circuit generator 7 which supplies a large short-circuit current i.sub.1 to the series connection S through an auxiliary circuit breaker 8 which is controlled by a breaker control circuit BC. Of all the interrupter units, the one 14 at the non-grounded end Sn alone is opened (alternatively a train of interrupter units may be opened) at a timing related to the phase of the current i.sub.1, to cause an arc in the interrupter unit 14. At a time point t.sub.1 when the instantaneous value of the current i.sub.1 becomes zero, a first high voltage source 9, being controlled by a voltage source control circuit VC, supplies a transient recovery voltage v.sub.1 for testing the interrupter unit, across the lead conductor 6 and the ground potential. Substantially simultaneously therewith, a second high voltage source 10, being controlled by the control circuit VC, supplies a voltage v.sub.2 across the tank 3 and the ground potential in a polarity reverse to v.sub.1. The magnitude of v.sub.2 is a difference between the whole restriking voltage v.sub.0 which is to be applied to all the interrupter units (11-14) and the transient recovery voltage v.sub.1 from the first high voltage source.
In this method, the whole transient recovery voltage v.sub.0 =.vertline.v.sub.1 .vertline.+.vertline.v.sub.2 .vertline. is applied across the space 15 between the ungrounded end of the series connection S and the tank, so that insulation of the space 15 and the performance of the interrupter unit 14 are simultaneously tested.
But when the insulation break-down of the space 15 occurs, the high voltage v.sub.2 from the second voltage source 10 is applied to the first voltage source 9 and may damage components provided in it. Such possibility is greater if a smaller number of the interrupter units are actually opened, i.e., if v.sub.2 /v.sub.1 is larger.